As social infrastructure, equipment such as water and wastewater systems, high-pressure chemistry pipelines for gas, petroleum, and the like, high-speed railways, long big bridges, superhigh-rise buildings, large passenger aircrafts, and vehicles is built. One of the important members of the equipment is pipes for passing fluid such as gas or water. In some cases, pipes may break due to deterioration or a natural disaster. When pipes break and the fluid leaks out, the broken part has to be repaired. For this purpose, there is a need to detect a leak of the fluid in the pipes. Hereinbelow, an inspection of the presence/absence of a leak of a fluid in pipes will be referred to as a leak inspection.
A general leak inspection is an auditory sensory inspection of listening for a leak sound by a person. In many cases, however, pipes are arranged under the ground or at a high place, and an inspection by manpower involves danger and great effort. To address the problem, devices performing a leak inspection have been proposed.
PTL1 discloses a method of detecting a pipe passing sound via microphones at both ends of an inspection interval, making detection signals taken by the microphones to be divided into a plurality of frequency bands by passing through a band-pass filter, obtaining a cross-correlation coefficient average of the frequency bands, and specifying a pipe leak point.
PTL2 discloses a method of disassembling a vibration signal caused by a water leak of a water pipe into a plurality of frequency components, evaluating a fluctuation amount with time of each of frequency components, and detecting the water leak of the water pipe.